1. Field of the Invention
The invention pertains to the field of control of valve timing in internal combustion engines. More particularly, the invention pertains to a device for varying the phase relationship between a camshaft and a camshaft drive.
2. Description of Related Art
A few modern engines today are equipped with variable cam phasers. The phasers move the cam position relative to the crankshaft, usually by using engine oil pressure. When the oil pressure is low, or at engine cranking, the phaser cannot move to the advance position because the cam mean torque is too high for the low oil pressure to overcome. If the engine was stopped in this state, the phaser would be in the wrong position.
Another problem is that prior-art oil-operated cam phasers are not self-locking. Therefore, the phase of the camshaft relative to the drive (timing belt, chain or gears coupling the camshaft to the crankshaft) is constantly moving, making it difficult to obtain and hold a correct positioning for the phaser.
One example of a phaser which does not use hydraulic pressure is Palmer""s xe2x80x9cTiming Device,xe2x80x9d U.S. Pat. No. 1,691,408, issued Nov. 13, 1928, which shows a manually adjustable cam sprocket with a worm gear that is fine tuned by a screw head for an internal combustion engine.
Another example is Papez""s xe2x80x9cControllable Camshaft for a Drive, Preferably an Internal Combustion Engine,xe2x80x9d U.S. Pat. No. 4,517,934, issued May 21, 1985, which shows an adjustment mechanism powered by an electric motor, driving a worm gear for the inner camshaft.
A third example is Suga""s xe2x80x9cValve Timing Control Apparatus,xe2x80x9d U.S. Pat. No. 5,156,119, issued Oct. 20, 1992, which shows a pair of worm gears shifting the phaser relative to the crankshaft using engine power. The worms are driven by an axial shifting plate, which is driven by friction wheels extending out of the phaser. The friction wheels rub on friction disks that are either in front or behind the phaser to rotate the two wheels one way or the other. A solenoid pulls or pushes on the mounting of the friction disks, pushing one way or the other against the two wheels.
Suga et al.""s xe2x80x9cValve Timing Control System for Internal Combustion Engine,xe2x80x9d U.S. Pat. No. 5,203,291, issued Apr. 20, 1993 shows an outer housing containing internal gear teeth, which are turned by small gears. The small gears are driven by a pin on the spiral cam, which is in turn on the gear shaft. A pair of stopper pins are also present to restrict the rotation of the gear when necessary.
Schiattino""s xe2x80x9cAutomatic Variator Valve Overlap or Timing and Valve Section,xe2x80x9d U.S. Pat. No. 5,355,849, issued Oct. 18, 1994, shows a worm gear driven by an electric motor, which turns or pushes a splined shaft. The turning or pushing of the shaft moves the camshaft axially to vary timing.
Pierik""s xe2x80x9cPlanetary Gear Phaser with Worm Electric Actuator,xe2x80x9d U.S. Pat. No. 5,680,837, issued Oct. 28, 1997, shows a worm gear driven by an electric motor outside of the phaser. The worm gear turns the sun gear of the phaser, which moves the camshaft position relative to the crankshaft.
Williams"" xe2x80x9cDevice for Controlling the Phased Displacement of Rotating Shafts,xe2x80x9d U.S. Pat. No. 4,747,375, issued May 31, 1998, describes a method of rotating a second cam that causes the resilient plunger like devices to exert a lateral force against wedge shaped valves, which causes a change in the valve lift and timing.
US published patent application US2001/0020460xe2x80x94xe2x80x9cApparatus for Adjusting a Camshaftxe2x80x9dxe2x80x94describes a phaser moved by planetary gearing, using an outer housing with sprocket outside and gearing inside.
US published patent application US2001/0020461xe2x80x94xe2x80x9cApparatus for Adjusting a Camshaftxe2x80x9dxe2x80x94uses three worm gears in a phaser. The worm gears are driven by six electromotors.
A phaser for adjusting the timing between a camshaft and a crankshaft. The phaser consists of an outer housing having internal and external teeth and an inner housing connected to the camshaft. The outer teeth couple to the cam drivexe2x80x94the timing chain, timing belt or timing gears. A worm mounted on the inner housing is meshed with the internal teeth of the outer housing. The worm gear is connected to one or two drive wheels, which are rotated by contact with stationary plates. The plates are moved by electromagnetic coils to contact the drive wheel or wheels, and turn them in one direction or the other. The actuators are activated by an engine control unit. The plates can be mounted concentrically on one side of the phaser, or on opposite sides.